Recognition of Emotional and Neutral Visual Scenes in Carriers of the MAOA, COMT, DRD4, and 5HT2A Gene Polymorphisms

Background It is known that some genes regulate neurochemical metabolism, and their polymorphisms affect cognitive performance, including the ability to categorize emotionally significant information. Objective The aim of our study was to analyze the recognition of emotional and neutral visual scenes in carriers of different polymorphic variants of the MAOA, COMT, DRD4, and 5HT2A genes. Design The study sample consisted of 87 university students (Caucasians, women 63%, average age 20.4±2.6 years). The genotypes of the COMT, 5HT2A, and DRD4 genes were determined by polymerase chain reaction. Agarose gel electrophoresis was used to determine the number of tandem repeats of the MAOA gene. Three hundred sixty (360) photographic images of scenes of different emotional valence (positive, negative, and neutral — 120 images for each category) were used as stimuli. These images were classified by expert assessments. The images were presented in a random sequence. The exposure time was 700 ms. The research participants were asked to determine the emotional valence of each scene. Results We found that only the COMT gene genotype affected the recognition of emotional and neutral visual scenes. Carriers of the COMT Val/Val genotype, which causes dopamine to stay in the synaptic space for a shorter time, are better in recognizing and demonstrate higher sensitivity to the emotional content of scenes. Carriers of the Val/Met genotype demonstrated the worst ability to differentiate the emotional valence of visual scenes. Conclusion This study has shown that the length of stay of monoamines in the synaptic space regulated by the COMT gene affects the recognition of emotional visual information.


Introduction
Visual scene recognition is one of the fundamental operations people use to build an internal model of the world. One of the important semantic characteristics of visual scenes is their emotional valence (You & Li, 2016). e individual features of recognition of emotional scenes a ect cognitive processes and are an important personal psychological characteristic (Bush et al., 2015). When a person's ability to recognize emotions is impaired (a condition called alexithymia), his/her ability to perceive negative visual scenes worsens .
In a study using EEG and fMRI simultaneously while the subjects were viewing visual scenes of pleasant, unpleasant, and neutral content, it was found that a ective scenes, depending on their valence, evoked speci c neural representations (Bo et al., 2021). e in uence of the scene's emotionality on the neuronal response was also shown using evoked potentials (Tebbe et al., 2021;Trujillo et al., 2021). ere was also evidence of valence-modulated susceptibility to the image distortions when observing the scenes (Stevenson et al., 2020).
Emotional scene recognition has both universal patterns and individual characteristics, which are determined by the person's genotype. In a study on 233 pairs of twins at the age of 11 years, it was discovered that the children's gaze trajectory during the perception of visual scenes was signi cantly in uenced by genetic factors (Kennedy et al., 2015).
Prior study has demonstrated that recognizing emotionally signi cant information is greatly in uenced by the activity of selective serotonin and noradrenaline reuptake inhibitors (Hamrer, 2012). e organization of these synaptic mechanisms is known to be largely genetically predetermined. In particular, the deletion of the ADRA2B gene that encodes the a2b-adrenergic receptor has been shown to increase reactivity to emotional stimuli (Li, 2013) and a ect emotional memory (Maheu et al., 2004;de Quervain et al., 2007;). However, the more obvious candidates for genes whose polymorphisms a ect the perception of emotionally signi cant information are those of the dopaminergic (DRD4, COMT) and serotonergic (MAOA, HTR2A) systems (Ermakov et al., 2017;Vorobyeva et al., 2020). e monoamine oxidase A (MAOA) gene is located on the X chromosome and regulates the duration of the dopamine, serotonin, and norepinephrine stay in the synaptic cle . Carriers of the MAOA gene alleles with two, three, and ve repeats in the promoter region have a low-active form of the gene and enzyme that catabolizes neurotransmitters, which leads to a longer stay of dopamine, norepinephrine, and serotonin in the synaptic cle ; carriers of alleles with 3.5, 4, and 3.5/4 repeats have a highly active monoamine oxidase A, which leads to a shorter stay of monoamines in the synaptic cle (Brady, 2012). Low-and high-activity genotypes for the MAOA-uVNTR are associated with the functioning of the mesolimbic subsystem of the dopamine system, cingulate gyrus, amygdala, nucleus accumbens, hippocampus, and prefrontal cortex. ere is also evidence that MAOA-uVNTR gene polymorphism is indirectly associated with the personal traits and processing of stimuli of various valences (Barnett et al., 2011;Williams et al., 2009). e COMT gene is located on chromosome 22. It encodes the production of the Catechol-O-methyltransferase enzyme, which plays an important role in the breakdown of catecholamines (dopamine, adrenaline, and norepinephrine). e single nucleotide polymorphism rs4860 (Val158Met) can be represented by the G allele encoding the amino acid valine, or the low active A allele encoding the amino acid methionine. Carriers of the A (Met) allele have an increased length of stay of the dopamine in the prefrontal cortex; they also have a higher pain threshold, lower stress resistance, and more e cient cognitive function. Carriers of the G (Val) allele, on the other hand, have decreased length of stay of catecholamines in the synaptic space due to the high activity of the COMT enzyme, as well as an increased sensitivity to pain, higher stress resistance, and a moderate decline in the prefrontal function (Chen et al., 2004;Lotta et al., 1995).
It has been shown that the Val158Met single nucleotide polymorphism of the COMT gene a ects individual di erences in attention, while insu cient or excessive catecholaminergic activity can each have equally undesirable consequences for attention span (Shalev et al., 2019). Serrano et al. have described the psychological characteristics (mainly related to the stress response) of carriers of di erent COMT genotypes (Serrano et al., 2019). It has been shown in a Russian sample that the presence of the Val/Val genotype in the COMT gene is associated with a high risk of depression (Gafarov et al., 2021). e DRD4 gene is located on chromosome 11. It encodes the D4 subtype of the dopamine receptor. e dopamine D4 receptor is involved in transmitting neural signals to the brain's mesolimbic system, which regulates emotions and complex behavior (Wang et al., 2017). e association of single nucleotide polymorphisms (SNPs) of the DRD4 gene with the functioning of working memory and perception was shown in a study on a South American family-based sample (Cervantes-Henriquez et al., 2021). e HTR2A gene that encodes the 5-HT2A receptor (5-hydroxytryptamine (serotonin) receptor 2A) is localized on the 13q14-q21 chromosome. is gene is involved in the serotonin system and is o en of interest to scientists who have been searching for genetic associations of various psychopathologies such as schizophrenia (González-Castro et al., 2013;Mistry et al., 2011;Yan et al., 2021), but the features of its relationship with emotional and cognitive processes in healthy people have not been su ciently studied.
Based on the above, we assumed that the described genes could be considered factors associated with human emotional reactions. However, in previous years, the relationship of these and a number of other genes with the perception of emotional scenes was studied mainly in connection with the development of pathological processes: a ective disorders (Cipriani et al., 2009) or Alzheimer's disease (Cavill, 2017). e aim of our study was to study the features of recognition of emotionally colored and neutral visual scenes in healthy carriers of the di erent genotypes of the MAOA, COMT, DRD4, and 5HT2A (HTR2A) genes.

Participants
Our study involved 87 university students (Caucasians, women 63%) ages 19 to 25 years (average age 20.4 ± 2.6). All participants had normal or normalized vision, and no history of neurological or psychiatric illness. At the initial stage of the process, all participants were informed about the research objectives and procedures, and gave written consent for voluntary participation.

Procedure
Stimuli ree hundred sixty (360) photographic images of scenes of di erent emotional valence (positive, negative, and neutral -120 images for each category) were used as stimuli. e images were obtained from open sources and classi ed as positive, negative, or neutral by independent experts. Selected scenes are freely available now as a dataset at https://osf.io/eagyc/. We aligned the images by average brightness and RMS contrast. e image width was 22.5, and the height was 18 angular degrees.

Procedure
Participants were positioned in a head-chin rest at 60 cm distance from the center of the screen. e images of the scenes were presented in a random sequence. e exposure time was 700 ms. Prior to the experiment, all subjects underwent brief training that helped familiarize them with the procedure and ensured that they understood the task correctly. e training images did not appear in the main experiment. e duration of the main experiment did not exceed 25 minutes, and the experimental task was not tiring. e subjects were tasked to recognize the emotional valence of each scene shown and report their decision by clicking one of the three response options (positive, negative, or neutral). e demonstration of the next stimulus was launched 100 ms a er the participant's response.

Genotyping
Genetic analysis was carried out in the "Biological Solutions and Technologies" laboratory (Russian Federation, Moscow). DNA was extracted from buccal cells. To determine the genotypes of the COMT, 5HT2A, and DRD4 genes, the genotyping procedure was carried out by using the real-time PCR method (Real-Time CFX96 Touch cycler, Bio-Rad, USA). An agarose gel electrophoresis procedure was used to determine the number of MAOA tandem repeats.
Statistical data analysis e number of correct recognitions and "false alarms" for each type of image was determined. Next, the sensitivity index (d') was calculated using the PAL_SDT_1AFC_ PHFtoDP function from the Palamedes toolbox (Prins & Kingdom, 2018). e probability of correctly identifying an emotion (hits) was considered as pH, and the probability of false alarms (fails) was considered as pF. For example, for a neutral im-age, pH is equal to the ratio of the number of "neutral" responses to stimuli expressing neutral scenes, to their total number; pF is the ratio of the number of "neutral" responses to positive and negative scenes, to the total number of such stimuli. e calculation comes down to subtracting the normalized pF from the pH for each type of stimulus (Prins & Kingdom, 2018). e overall (general) sensitivity index was calculated as the average d' for the three types of scenes.
For intergroup comparisons of index sensitivity in carriers of di erent genotypes of the studied genes, we used the Kruskal-Wallis Test. As a post-hoc procedure, Dunn's test with Holm's correction for multiple comparisons was used. Statistical data processing was carried out using an open-sourced JASP Computer so ware (Version 0.16, 2021).

Results
We have analyzed the following DNA sections: the Val158Met polymorphic locus of the COMT gene (472A>G, rs4680), tandem repeats (VNTR) in the promoter region of the MAOA gene, the HTR2A gene for the 5HT2A serotonin receptor (T102C rs6313, Tr3) and the DRD4 gene for D4 subtype dopamine receptor (\-C-521T, rs1800955). e following genotypes were found in our sample for the MAOA gene: highly active H genotypes, including 4 tandem repeats (VNTR) of the promoter region of the gene; low-active L genotypes with 5 tandem repeats (VNTR) of the promoter region of the gene; and heterozygous medium active genotypes M, including alleles with 5 and 4 tandem repeats (VNTR) of the promoter region of the gene. e distribution of genotype frequencies of the studied genes is presented in Table 1 and corresponds to the Hardy-Weinberg equilibrium.). Table 1 Frequency distribution of MAOA, COMT, DRD4, and 5HT2A gene genotypes in the study sample

Gene polymorphisms Genotypes and their distribution in the sample (in percents)
Gene We proceeded to the main part of the study a er processing the results of the genetic analysis. Table 2 shows the di erences in the accuracy of recognition of the emotional content of visual scenes in carriers of di erent genotypes of the MAOA, COMT, DRD4, and 5HT2A genes. e Kruskal-Wallis Test showed signi cant di erences in sensitivity to the neutral scenes in carriers of di erent COMT gene genotypes (H = 9.1, df = 2, p = 0.01).
e Dunn's Post Hoc Comparisons showed that carriers of the heterozygous genotype were less successful at recognizing neutral images (Figure 1). At the same time, the recognition accuracy of neutral scenes in Val/Met was statistically signi cantly lower than in Val/Val (VM -VV, z = -2.798, p holm = 0.008).
e Kruskal-Wallis Test showed signi cant di erences in sensitivity to the emotional valence of scenes by carriers of di erent COMT gene genotypes (H = 7.458, df = 2, p = 0.02). Dunn's Post Hoc Comparisons showed that carriers of the Val/Val genotype were generally better than others in recognizing the emotional valence of stimuli (Figure 2). At the same time, the accuracy of recognition of the emotional valence of scenes in Val/Val was statistically signi cantly higher than in Val/Met (VM -VV, z = -2.692, p holm = 0.011).

Discussion
Our results show that of the four genes studied, only COMT polymorphism was associated with the perception of emotional visual scenes. Moreover, statistically signi cant di erences were obtained only when comparing the Val/Val and Val/Met groups. It turned out, in particular, that carriers of the Val/Met genotype for the COMT gene were worse in recognizing neutral and emotional scenes than carriers of the Val/Val genotype.
Our nding is consistent with the results of a previous meta-analysis, which showed an association of the Met allele with reduced emotional processing e ciency (Mier et al., 2010). A more recent study discovered that Val/Met heterozygotes retain fewer details of past emotional events than carriers of other genotypes (Tõugu et al., 2021). What can explain it? It is possible that the length of stay of monoamines in the synaptic space, which is regulated by the COMT gene, is causing those di erences. A number of authors have posited that carriers of the Val/Met COMT genotype have  a longer stay of monoamines in the synaptic space compared to carriers of the Val/Val genotype (Chen et al., 2004;Lotta et al., 1995). Our results indicate that a longer stay of monoamines in the synaptic space is a less preferable factor in tasks for recognizing the emotional valence of visual scenes. e decline in scene categorization performance in Val/Met carriers may also be associated with increased levels of dopamine in the prefrontal cortex. Analysis of the data presented by Zareyan et al. (2021) indicates that the presence of the Met allele at codon 158 results in higher levels of dopamine in this cortical region than the presence of the Val allele does. It is possible that successful recognition of neutral and emotional visual scenes does not require an increased amount of dopamine in the prefrontal cortex. On the contrary, its increased levels worsen the performance.
us, the greater sensitivity of carriers of the Val/Val COMT genotype to the emotional content of visual scenes may be associated with a faster breakdown of monoamines (including dopamine) in the synaptic space, as well as with a relatively low level of dopamine in the prefrontal cortex.

Conclusion
is study, carried out on healthy subjects, made it possible to obtain new data concerning the mechanisms of recognition of emotional visual information and the inuence of genes involved in the regulation of neurochemical metabolism on these processes. Our results specify the role of the COMT gene polymorphism in the perception of emotionally signi cant signals and allow us to draw the following conclusions: 1. Among the examined genes (MAOA, COMT, DRD4, and 5HT2A), only the COMT gene genotype affects the recognition of emotional and neutral visual scenes. 2. Carriers of the COMT Val/Val genotype, which causes dopamine to stay in the synaptic cleft for a shorter time, recognize neutral scenes better and demonstrate a higher sensitivity to the emotional content of scenes. 3. Carriers of the COMT Val/Met genotype are less successful at recognizing the emotional valence of visual scenes.
Limitations e limitation of our study is related to the unequal number of persons per genotype in the sample. However, such unevenness of genotypes occurs naturally in the human population.

Ethics Statement
All participants were informed about the research objectives and procedures and gave written consent for participation. e study was approved by the local ethics committee and conducted in accordance with the ethical standards of e Code of Ethics of the World Medical Association (Declaration of Helsinki).

Author Contributions
P.E. conceived of the idea and analyzed the results. E.V. conducted a theoretical analysis of the problem and analyzed the results. E.D. managed the data collection, translated, reviewed, and edited the nal version of the manuscript. V.B. determined and veri ed the research methods, and reviewed and edited the nal version of the manuscript. E.K. compiled a database of stimuli and participated in the analysis of the results obtained. D.A. compiled a database of stimuli and participated in the data collection. All authors discussed the results and contributed to the nal manuscript.

Con ict of Interest
e authors declare no con ict of interest.